Is there any way to create a not constrained many-to-one mapping which is lazy?

It is not very effecient (or pretty) to catch ObjectNotFound exceptions throughout our code, and we have several relations which are not constrained by foreign keys (and thus may not exist).

I don't know how to do this, but I was thinking that if a direct relation couldnt be mapped then something like:
originalObject.getMappedClass().getActuallyMappedClass()
would also be ok if a trick like that could make a non-constrained lazy mapping work.

Any ideas/Suggestions?

Thanks